Effects of lorazepam on saccadic eye movements - evidence from prosaccade and free viewing tasks

Rationale: Peak velocities of saccadic eye movements are reduced after benzodiazepine administration. Even though this is an established effect, past research has only examined it in horizontal prosaccade tasks. Objectives: The spectrum of saccadic eye movements, however, is much larger. Therefore, we aimed to make a first attempt at filling this research gap by testing benzodiazepine effects on saccades under different experimental task conditions. Methods: 1 mg lorazepam or placebo was administered (within-subjects, double-blind, in randomised order) to n = 30 healthy adults. Participants performed an extended version of the prosaccade task, including vertical saccade directions and different stimulus eccentricities, as well as a free viewing task. Results: Results from the prosaccade task confirmed established effects of benzodiazepines as well as saccade direction on saccadic parameters but additionally showed that the drug effect on peak velocity was independent of saccade direction. Remarkably, in the free viewing task peak velocities as well as other saccade parameters were unaffected by lorazepam. Furthermore, exploration patterns during free viewing did not change under lorazepam. Conclusions: Overall, our findings further consolidate the peak velocity of prosaccades as a biomarker of sedation. Additionally, we suggest that sedative effects of low doses of benzodiazepines may be compensated in tasks that more closely resemble natural eye movement behaviour, possibly due to the lack of time constraints or via neurophysiological processes related to volition.